The present invention relates to the art of diagnostic imaging. It finds particular application in connection with spiral volume imaging using CT scanners and will be described with particular reference thereto. It is to be appreciated that the present invention will also find application in connection with other types of volume imaging of human patients for medical diagnostic purposes or manufactured articles to detect internal structures or flaws and the like.
In conventional spiral or helical scanning, an x-ray source or tube emits a fan beam of radiation as it rotates continuously around an examination area as a subject support table moves therethrough at a constant, linear velocity. Detectors positioned across the examination region from the x-ray tube convert x-rays which traverse the subject patient into corresponding electronic data. The collected data effectively represents a helical path of constant pitch through the subject or patient. The helical data is reconstructed into a volumetric image representation, typically a series of consecutive thin slice images of the patient.
One technique for reconstructing image slices from the stored spiral data involves interpolating collected spiral data into planar data. For example, for each plane transverse to a central axis, corresponding rays in the two closest spirals to either side of the plane are interpolated to generate one of the rays of the planar data set. This same interpolating procedure is repeated for each ray of a complete data set, e.g. a data set extending over 180.degree.. The data from the transverse plane is reconstructed into a planar or thin slice image representation of the volume image representation using conventional reconstruction techniques.
Heretofore, partial volume artifacts have degraded CT scanner image quality. Prior art techniques have attempted to reduce the adverse effects caused by partial volume artifacts by combining several of the reconstructed thin slice images. Two or more adjacent thin slice images are combined or summed to form a single thick slice image with reduced partial volume artifact effects.
Combining thin slice images has the benefit of retaining low contrast resolution, but suffers from possible motion artifacts due to the long acquisition time for each summed image as well as the additional reconstruction time to generate the several thin slice images prior to combination.
When six thin slice images are combined to reduce partial volume artifacts in the resulting slice representation, six reconstruction operations are first performed. The length of time to perform six reconstructions and combine the resultant six thin slice images into a partial volume artifact reduced thicker slice image causes a significant delay.
The present application contemplates a new and improved scanning technique which overcomes the above referenced problems and others.